1. Field of the Invention
The present invention relates to an electron emission material including a carbon material and a method of manufacturing the same. The present invention also relates to an electron emission element including the electron emission material used therein.
2. Description of the Related Art
Materials including a carbon material such as amorphous carbon, diamond, carbon nanotube (CNT), fullerene, etc. have been developed actively as electron emission materials that are used for electron sources of various devices such as displays, etc. For instance, the CNT is excellent in electroconductivity and heat resistance. Furthermore, as described in “Carbon Nanotube, Challenge to Nanodevice, p 175–184, published by Kagaku-Dojin Publishing Company. INC (January 2001)”, since the CNT has a high aspect ratio (length/diameter) and allows an electric field to be concentrated, it is excellent in electron emission characteristics. Hence, it is expected to be applied to electron sources that can be driven at a lower voltage. The CNT, however, has problems in manufacturing cost, mass-productivity, stability in the case of long-term use, etc.
On the other hand, the improvement in electron emission characteristics has been attempted not by utilizing the peculiar shape of the material as in the case of the CNT but by changing the properties of the surface of the material. For example, H10(1998)-188778A/JP discloses a technique of improving the electron emission characteristics by disposing a metallic element having a small work function on the surface of a carbon material through oxygen to change the electronic state of the surface. The carbon material disclosed in H10(1998)-188778A/JP is a particle produced by forming a carbon body using a fine particle of a metal catalyst as a nucleus and then allowing the surface of the carbon body thus formed to terminate with an alkali metal element or an alkaline earth metal element. In such a material, since the metallic fine particle has a large size and thus has a small interaction with carbon, it is difficult to change the electronic state of the carbon surface satisfactorily. Accordingly, it is difficult for the material to provide a high emission current density as an electron source.
Furthermore, for instance, 2003-53167A/JP discloses a film-like carbon material containing a metallic element (a carbon film containing a metallic element). The carbon material disclosed in 2003-53167A/JP is formed by introducing a metallic element into a solution of organic polymer, forming a polymer film, and then baking the polymer film thus formed. The metallic element to be introduced is an element that belongs to Group 8 to Group 12 (Group of the element is indicated according to the prescription of IUPAC(1989) in the present specification) such as Fe, Co, Ni, Pd, Pt, Cu, Ag, Zn, Cd, etc. The baking temperature is in the range of 500° C. to 1200° C. Such a carbon material is excellent in gas separation characteristics. However, the metallic elements of Group 8 to Group 12 conceivably do not contribute to the change in the electronic state of the carbon material surface that depends on the interaction with carbon. Accordingly, in the case of the carbon material disclosed in 2003-53167A/JP, it is difficult to improve the electron emission characteristics.
In addition, H05(1993)-170536A/JP and 2002-274827A/JP, which are documents relating to the present application, disclose techniques of adding a metallic compound to a polyamic acid. In these documents, however, the metallic compound to be added to a polyamic acid is a chloride (Lines 39 to 47, Column 20 of H05(1993)-170536A/JP) and an inorganic phosphate compound (Line 48, Column 4 to Line 8, Column 5 of 2002-274827A/JP). It is difficult for such metallic compounds to satisfactorily change the electronic state of the carbon material that depends on the interaction with carbon and thus to improve the electron emission characteristics. Furthermore, these documents refer to no electron emission material.